The grooved nucleus. A useful diagnostic criterion of papillary carcinoma of the thyroid.

The optically clear nucleus has been recognized widely as an important histological feature of papillary carcinoma of the thyroid, and it is now considered by many workers as standing on an equal basis with the papillae for the diagnosis of this tumor. However, clear nuclei are sometimes patchy in distribution or absent in papillary carcinoma, and may be difficult to differentiate from pseudoclear nuclei which may be found in a variety of thyroid lesions. This study was undertaken to determine whether the grooving of the nuclei, a well-recognized electron-microscopic feature, can serve as an additional reliable light microscopic diagnostic criterion of papillary carcinoma. The histological sections of 103 consecutive cases of thyroid carcinoma, (including 89 cases of papillary carcinoma), 100 consecutive noncancer thyroidectomy specimens, and five cases of Hashimoto's thyroiditis were reviewed. Grooved nuclei were found in all cases of papillary carcinoma in almost every high-power microscopic field, and in the two cases of poorly differentiated thyroid carcinoma. Similar nuclei were found in only a very occasional field in four cases of adenoma, and one case each of multinodular goiter and Hashimoto's thyroiditis. We conclude that the deep grooving of the nuclei is a useful cytological feature for the diagnosis of papillary thyroid carcinoma.